Brenda Ross

High refractive index immersion fluids for 193 nm immersion lithography

For the next-generation immersion lithography technology, there is a growing interest in the immersion fluids having a refractive index larger than 1.5 and low absorbance at 193nm wavelength. In this paper, we report our effort in identifying new immersion fluid candidates. The absolute refractive index values and thermo-optic coefficients, dn/dT, were measured with 1x10-4 and 1x10-5 accuracy respectively at 193nm wavelength. The results showed promising candidates having refractive index ranging from 1.5 to 1.65 with low absorbance at 193nm wavelength. Preliminary imaging results with a new immersion fluid gave good 65nm Line/Space patterns. However, the minimum exposure time of 20sec is about ten times as needed for water, indicating the need to further reduce the absorbance of the immersion fluid.

Combined pattern collapse and LWR control at the 70 nm node through application of novel surface conditioner solutions

As pattern collapse and line width roughness (LWR) become critical lithography challenges, there is growing interest in applying surface conditioner solutions during the post-develop process to address BOTH these issues. In this paper, we patterned 90nm 1:1.2 lines/spaces (L/S) on 200mm wafers and 70nm dense lines on 300mm wafers to evaluate the combined performance of pattern collapse and LWR using newly formulated surface conditioners. The performance of each conditioner was compared to the standard formulation, which is capable of significant pattern collapse reduction, but affords no LWR improvement. These newly improved formulations enabled a ~20% LWR reduction for 90nm features and a ~10% LWR reduction for 70nm dense lines. In addition, the new formulations significantly enlarged the LWR and CD process windows for 70nm dense lines, as demonstrated by a 50% increase of maximum depth of focus (DOF) over the standard formulation.

Surface conditioning solutions to reduce resist line roughness

In this study, surface conditioning solutions were used during post-develop process to enhance the 193 nm lithography performance. These solutions were applied to the wafer surface in a surface treatment step between the DI water rinse and drying steps. Compared to the standard develop process, the formulated surface conditioning solution enabled a 24% reduction in line width roughness, particularly in the high frequency roughness components. The solution also improved the pattern collapse performance by enlarging the non-collapse window and extending the minimum CD feature size by 10 nm. Additional benefits provided by the formulated surface conditioner solution were minimal changes to CD and resist profile.

Pattern collapse and line width roughness reduction by surface conditioner solutions for 248-nm lithography

In this paper, surface conditioners were applied during the post-develop process to extend the capability of 248nm lithography processing below the k1= 0.30 threshold. The interaction between surface conditioner and photoresist was found to be a critical parameter in affecting pattern collapse, line width roughness (LWR), and process latitude. Tailoring the surface interaction properties required balancing between surface conditioners that had weak interactions that improved pattern collapse only marginally, to surface conditions with strong interactions that produced a considerable reduction in LWR but provided no benefit to pattern collapse or process latitude when compared to DI water. The surface conditioners with optimized resist interactions provided significant improvement in all performance parameters including reduced pattern collapse, improved LWR, and enlarged usable process latitude.

Surface conditioning solutions for pattern collapse reduction

Recently, there has been a growing interest in using surface conditioning solutions to solve the pattern collapse challenge. In this study, we investigated both pattern collapse and defect performance of surface conditioning solutions on multiple 193 nm resist systems. While the surface conditioning solutions were able to reduce the pattern collapse with good defect control with a majority of resist systems, it can increase the defect level on certain resist. Shortening the surface treatment step and optimizing the formulation can reduce the defect counts to the control level without compromising pattern collapse performance. This study also demonstrated that the surface conditioning solution is compatible with 248 nm processing, enabling the patterning of 90 nm 1:1.2 pitch lines.

Impact of surfactant in developer and rinse solution on 193-nm lithography performance

In this study, surfactant-formulated developer and rinse solutions were used to enhance the performance of a 193 nm lithography process. The wetting and interfacial characteristics of surfactant-formulated solutions were studied and utilized as a screening tool for optimum formulation. The selected formulation was compared to the non-formulated TMAH development and DI water rinse process. Surfactants in developer and rinse solution significantly reduced pattern collapse, enabling an 86% increase of critical normalized aspect ratio. This corresponds to an increase in the usable resist thickness for an 80 nm 1:1 feature from 179 nm to 332 nm. Additional benefit provided by surfactant formulated process was a 25% improvement on both within-wafer and wafer-to-wafer critical dimension uniformity.

Linewidth roughness reduction at the 55 nm node through combination of classical process optimization and application of surface conditioner solutions

In this paper, the standard ASML process was optimized to reduce LineWidth Roughness (LWR) while minimizing the impact on other process performance criteria such as Depth Of Focus (DOF) and Exposure Latitude (EL). The impact of classical process optimization parameters such as post exposure bake temperature and post exposure bake time were investigated together with less often varied parameters such as hard bake temperature. These parameters were studied in conjunction with novel surface conditioners to reduce LWR. The results show that a significant reduction in the LWR number can be obtained by combining the application of a dedicated surface conditioner solution with the fine tuning of other parameters such as post exposure bake and hard bake temperature. Several process parameters had to be tuned simultaneously to retain a decent process window for the fine tuned process although some EL had to be sacrificed.